Aircraft designers and manufacturers are under continual pressure to reduce the aerodynamic drag on aircraft surfaces, so as to increase aircraft performance and/or to reduce aircraft fuel consumption. Aircraft are generally designed with gentle curves and smooth surfaces to enable laminar air flow over extended surface areas in order to decrease drag, thereby increasing overall fuel efficiency of the aircraft while in flight.
A significant amount of aircraft drag is caused by boundary layers that build up on the exposed surfaces of the aircraft during flight. A boundary layer is a thin layer of low velocity, low dynamic pressure air located near a solid boundary and resulting from the air being at rest at the interface with the solid boundary. The boundary layer build-up on the aircraft wings and/or other external surfaces causes skin friction and therefore significantly contributes to airplane drag. Because laminar boundary layers create less friction at the aircraft surfaces than do turbulent boundary layers, one technique for reducing aircraft drag is to establish and to preserve a laminar boundary layer over a significant portion of the external surfaces of the aircraft.
On some aircraft, porous or perforated outer layers have been used on surfaces and leading edges of wings, vertical/horizontal, stabilizers and engine nacelles to enhance laminar flow over a corresponding portion of the external surface of the aircraft. This method preserves the laminar boundary layer by removing a small amount of the low momentum boundary layer air through the exposed flow surface via a distributed suction system.
Aircraft also contain internal heat generating components and systems, such as power electronics, multifunction fuel cell power Systems (“MFFCS”), auxiliary power units (“APUs”) and main engines. Typically, aircraft dissipate excess heat to the atmosphere through heat exchangers. These heat exchangers tend to be heavy, which reduces available transport capacity of the aircraft, especially if the temperature differential between the hot and cold working media of the heat exchanger is small.